The present invention relates to the ultra small-sized chip type light emitting device using a light emitting diode (LED) chip which can obtain the symmetric luminous intensity distribution in a longitudinal direction on a board and can enhance wire bonding reliability.
A small-sized chip type light emitting device with a light emitting diode (LED) chip is known as a conventional light emitting source. FIG. 2 is a perspective view showing an example of such chip type light emitting device. FIG. 2 illustrates that a pair of electrode patterns 3 and 4 comprised of conductive layer such as copper (Cu) plate layer is formed at the both ends of the board 2. One electrode pattern 3 consists of the surface electrode 3a, side face electrode 3b and back electrode 3c. 
The other electrode pattern 4 also consists of the surface electrode 4a, side face electrode 4b and back electrode 4c. The side face electrode 3b and side face electrode 4b of a pair of electrode patterns 3 and 4 form several elliptical through holes in parallel on an original large-sized board on which the board 2 can be obtained by dividing, the internal surface of the elliptical though holes is plated with Cu, etc., and the surface electrodes 3a/4a and back electrodes 3c/4c of a pair of electrode patterns 3 and 4 are connected to each other.
The pad 3p is formed on the surface electrode 3a of one electrode pattern 3 and the LED chip 1 is mounted there by die-bonding. One end 5a of the metal wire 5 is connected electrically to the electrode 1a of the LED chip 1 by wire bonding. The other end 5b of the metal wire 5 is connected electrically to the surface electrode 4a of the other electrode pattern 4 by wire bonding. The ultrasonic wave is used in this wire bonding.
The LED chip 1 mounted on the board 2, in which the lower electrode is connected to the surface electrode 3a of one electrode pattern 3 by the wiring bonding, and the metal wire 5 connected electrically to the upper electrode 1a of the LED chip 1 and to the surface electrode 4a of the other electrode pattern 4 by wire bonding are sealed with the translucent resin mold 6. The positions of both ends of this translucent resin mold 6 are located separately from each other at the inside of both ends of the board 2. The chip type light emitting device 20 is formed as mentioned above.
At the handling such as transportation, etc. for automatic mounting to a printed board, etc., the translucent resin mold 6 is picked up by a chuck and the chip type light emitting device 20 is transferred. In the configuration shown in FIG. 2, both ends of the translucent resin mold 6 are located at the inside of the surface electrodes 3a and 4a of a pair of electrode patterns 3 and 4. Therefore, the length of the translucent resin mold 6 is shorter than that of the board 2 of the chip type light emitting device 20, and the contact area for picking up becomes smaller, so if the size of the board 2 becomes 1.6 mm (length)xc3x970.8 mm (width) or less, the handling cannot be performed smoothly.
FIG. 3 and FIG. 4 are perspective views showing an example of conventional another chip type light emitting device and the example illustrates that the semi-circular notches 7 and 8 have been formed at both ends of the board 2. FIG. 5 is a characteristics diagram showing the distribution of luminous intensity I of the chip type light emitting device of FIG. 3. In FIG. 3 and FIG. 4, the same places as FIG. 2 or the points corresponding to FIG. 2 are marked with the same symbols. In the example of FIG. 3, the side face electrodes 3b and 4b of a pair of electrode patterns 3 and 4 are formed at the internal face of the semi-circular notches 7 and 8 which are formed at both ends of the board 2.
The surface electrodes 3a and 4a of a pair of electrode patterns 3 and 4 extend to a place where those electrodes cover the upper faces of the notches 7 and 8 and both ends of the translucent resin mold 6 and both longitudinal ends of the board 2 are aligned. In the example of FIG. 3, the surfaces of the notches 7 and 8 are covered with the surface electrodes 3a and 4a of a pair of electrode patterns 3 and 4. Therefore, the resin does not flow into the notches 7 and 8 when the translucent resin mold 6 is processed.
In the example of FIG. 3, both ends of the translucent resin mold 6 are located at both longitudinal ends of the board 2. Therefore, this example has the advantage of securing the surface area of the translucent resin mold 6 to the extent that the said handling can be performed smoothly even if the chip type light emitting device 30 is downsized.
However, assuming that both ends of the translucent resin mold 6 are located at both longitudinal ends of the board 2 as shown in FIG. 3, if the board size becomes small, e.g., 1.6 mmxc3x970.8 mm, the LED chip cannot be centered on the board 2 as shown in FIG. 4.
In the example of chip type light emitting device 40 of FIG. 4, the LED chip 1 is mounted at a position shifted to a longitudinal center of the board 2 and the other end 5b of the metal wire 5 is bonded at a position close to the end of the board 2. That is, the other end 5b of the metal wire 5 is bonded at a position where the surface electrode 4b of the electrode pattern 4 covers the notch 8.
As described above, a position to bond the other end 5b of the metal wire is located on the surface electrode 4b which covers the upper face of the notch 8. Therefore, the notch 8 is located under a place where wire bonding is performed and the mechanical strength of horn support deteriorates at wire bonding with the ultrasonic wave.
Therefore, enough pressure cannot be applied to the horn which propagates the ultrasonic wave at the ultrasonic wave processing and the surface electrodes 4b of the electrode pattern 5 and the other end 5b of the metal wire cannot be bonded completely to each other by the ultrasonic wave. To enhance the reliability of bonding with the ultrasonic wave, the configuration illustrated in FIG. 3 is adopted. However, in FIG. 3, the LED chip 1 is mounted at the off-centered position on the board 2.
In the example of FIG. 3, the LED chip 1 cannot be centered on the board 2. As a result, the LED chip 1 is located at the decentered position on the translucent resin mold 6 also. So, as shown in the luminous intensity characteristics diagram of FIG. 5, there was a problem that the symmetric luminous intensity distribution cannot be obtained in a longitudinal direction of the board.
The present invention was made taking such problem into consideration and the purpose of the present invention is to offer the ultra small-sized chip type light emitting device which can obtain the symmetric luminous intensity distribution in a longitudinal direction of the board even if the board is downsized and which can enhance wire bonding reliability.
The chip type light emitting device offered by the present invention comprising: a board of nearly rectangular shape in a plane view; first and second electrode patterns formed at both ends of a surface of the board; a light emitting diode (LED) chip mounted on the first electrode pattern; a metal wire connected to the LED chip and the second electrode pattern by wire bonding; and a translucent resin mold which seals the LED chip and the metal wire;
wherein one notch is formed at one end of the board at the first electrode pattern side and two notches are formed at both sides of the other end of the board at the second electrode pattern side, and the positions at both ends of the translucent resin mold are arranged to the positions at both ends in a longitudinal direction of the board.
The preferred embodiment of the present invention features that the LED is almost centered on the board.
The preferred embodiment of the present invention features that the board size is 1.6 mmxc3x970.8 mm or less.
The preferred embodiment of the present invention features that the metal wire is connected to the LED chip and the surface electrode of the second electrode pattern, which is located between the two notches formed at both sides of the other end of the board at the second electrode pattern side, by wire bonding.
The preferred embodiment of the present invention features that one notch formed at the one end of the board at the first electrode pattern side is semi-cylindrical and the two notches formed at both sides of the other end of the board at the second electrode pattern side are quarter-cylindrical.
According to the present invention, two notches are formed at both side of one end of the board. Therefore, even if a wire bonding position is close to the end of the board, wire bonding of the second electrode pattern and metal wire is made stably on the bard between such two notches and the LED chip can be centered on the board. Therefore, the ideal symmetric luminous intensity characteristics can be obtained in a longitudinal direction of the board.
One notch is formed at one end of the board and two notches are formed at the other end. So, the polarity of the LED chip can be checked easily. If the translucent resin mold is milk white, the LED chip embedded in the translucent resin mold is illegible. However, one notch is formed at one end of the board and two notches are formed at the other end. Therefore, it is obvious that the electrode structure is asymmetric and the polarity can be checked easily because of the appearance of chip type light emitting device.
Moreover, the positions of both ends of translucent resin mold are arranged to the positions of both ends in a longitudinal direction of the board. Therefore, the contact area for picking up can be increased and handling process can be performed smoothly to ultra small-sized chip type light emitting device.